The invention relates to an energy absorbing element and to a bumper system for vehicles that includes the energy absorbing element, which serves for the transmission and absorption of kinetic energy released, for example, in the event of motor vehicle accidents. The energy absorbing element is particularly suitable in vehicle bumper systems, but may equally serve as part of another vehicle structure and other safety elements, having a comparable requirement profile.
Energy-transmitting and energy-converting systems, particularly or use in the area of vehicle bumpers, are known and are successfully employed. Bumper systems which survive minor accidents (at an impact speed of up to about 8 km/h) without damage owing to energy-absorbing elements are widespread. In order to achieve favorable risk ratings with vehicle insurers, shock-absorbing systems which can be loaded significantly above a crash speed of 10 km/h are sought by many vehicles manufacturers. In the USA, bumper systems with a damage-free crash speed of up to 8 km/h are generally employed. If the energy introduced into the system is even greater, for example in the Allianz Zentrum fxc3xcr Technik (Central Alliance for Technologyxe2x80x94AZT) crash test at a speed of 15 km/h, the energy is absorbed by special energy absorbing elements.
As a general rule, the installation space available for the known systems mentioned is very small. The high kinetic energy to be converted in a damage event requires a high efficiency of the system, i.e., an energy absorbing element with force-deformation characteristics as ideal as possible. This ideal characteristic is notable for the fact that, after an initially steep rise in force while the energy absorption progresses in time, a horizontal plateau with a constant force occurs. The energy absorbed here is defined as the area below the force-displacement curve and this area should be as large as possible.
In energy absorption, a distinction can be made between so-called reversible and non-reversible systems. Examples of reversible systems which may be mentioned are those with hydraulic dampers (e.g., gas-filled springs). These systems are very efficient and convert the energy of an impact efficiently. The disadvantage of the hydraulic damping systems is their complex and typically very costly production, which prevents these systems from being used widespread.
Examples of non-reversible systems include support systems made of steel or aluminum with plastically deformable steel or aluminum elements for energy absorption. For relatively low energies to be converted, quasi-reversible systems may be employed (e.g., foam blocks made of energy absorption (EA) foam or aluminum foam). If a great energy is to be absorbed, deformable sheet-metal profiles are generally employed.
Apart from pure energy conversion, the absorption systems typically must fulfill other requirements. Independence from climate and weather influences, high reproducibility of the energy conversion, ease of maintenance on replacing the systems and tolerance compensation on mounting are also important requirements.
The object on which the invention is based is to develop an energy transmission and absorption system which converts the kinetic energy (for the most part into heat) from moving vehicle masses in the smallest possible space by means of the plastic deformation of a material or element. This system should be easy to handle and, particularly when fitted to a vehicle, should enable positioning (e.g., tolerance compensation) in all three spatial directions (i.e., the x, y and z spatial directions). Furthermore, it should exhibit substantially reproducible behavior over its entire period of use, be cost-effectively producible and be lightweight.
Apart from pure energy conversion, the system is to be capable of distributing the forces, e.g., from an impact, to the adjoining structures. The system should also stabilize the body or frame structure of vehicle during an impact event.
An energy absorption element which fulfills the above-mentioned requirements with regard to ease of fabrication, lightness and energy absorption behavior has been found. Specifically, a bumper system has been developed which, owing to the particular arrangement of a transverse beam and energy absorption elements (and the special shape of the latter), is capable of absorbing the energy of an impact with very high efficiency over a preset deformation distance. In particular, owing to the lateral arrangement of energy absorbing elements with respect to the transverse beam, this system provides a much greater distance for energy conversion than conventional systems with an energy absorbing element arranged behind a transverse beam.
In accordance with the present invention, there is provided an energy absorbing element (2, 2xe2x80x2) comprising:
(a) at least two oppositely arranged metal sheets (7, 8) having a multiplicity of predetermined buckling points (11, 12 and 13) which enable each sheet to fold up along its longitudinal direction (e.g., in the x-direction); and
(b) a plurality of connecting ribs (9) which interconnect said oppositely arranged metal sheets (7, 8), said connecting ribs (9) comprising a plastic material selected from at least one of thermoplastic material and thermosetting plastic material.
The features that characterize the present invention are pointed out with particularity in the claims, which are annexed to and form a part of this disclosure. These and other features of the invention, its operating advantages and the specific objects obtained by its use will be more fully understood from the following detailed description and the accompanying drawings in which preferred embodiments of the invention are illustrated and described.
Other than in the examples, or where otherwise indicated, all numbers or expressions, such a those expressing structural dimensions, etc, used in the specification and claims are to be under stood as modified in all instances by the term xe2x80x9cabout.xe2x80x9d